Since October 14, when a bulldozer operator helping to dig a new water reservoir stumbled across bones from an ancient Columbian mammoth, researchers have unearthed what they call one of the most significant fossil discoveries in Colorado history.

"Every day blows us away," said paleontologist Ian Miller of the Denver Museum of Nature and Science. "It's one of the most exciting paleontological moments of my life. It's unprecedented in Colorado, and may turn out to be unprecedented in the American West."

So far, crews have excavated the prehistoric bones of mammoths, mastodons, ice age deer and ground sloths, from the site of an ancient lake the animals likely used as a watering hole. The reservoir at the ski resort was being dug to help store water used for making snow.

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"The reason there's a whole bunch of animals here is that a hole in the ground like this that fills with water and mud at the bottom, is a great place to preserve stuff for a long period of time," Miller said.

Columbian mammoths roamed North America during the ice age. The largest ranged from about 12 to 13 feet high and weighed up to ten tons. Mastodons, which are distant cousins to mammoths and elephants, stood about eight to ten feet tall and could weigh around eight to ten tons.

Animal Fossils Possibly 100,000 Years Old

Scientists originally thought the bones ranged in age from about 12,000 to 16,000 years old. But a weekend discovery of horns and a skull from an ice age bison has scientists rethinking that timeline.

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"We really are starting to think that this think may be as old as 100,000 years," Miller said.

The bones — along with ancient plants that still have traces of green after millennia have passed — are considered original material. They are so well preserved that scientists plan on extracting the ancient DNA that will give clues about a range of subjects, including how the animals evolved and the composition of Earth's ancient climate.

"We'll have a nice continuous record of climate change here in Colorado that will be directly tied to a global dataset of climate change," Miller said.

The dig is being overseen by the Denver museum, in conjunction with a team of researchers from around the country who have now descended on the site.

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Pennsaylvia man finds 300-year-old fossil

"In 40 years I have excavated a lot of archeological sites," said Steve Holen, the curator of archaeology at the Denver museum. "In my life I have never been more excited to find a site like this."